For this exercise you are going to use the Vortex Following option, which tracks the center of low pressure in a tropical cyclone, and allows the nested domain to move inside the parent as the cyclone moves. This can be useful because tropical cyclones typically move over a large area over time. Instead of having to make a very large parent domain, with a large high-resolution nest (which can be computationally expensive), you can just track the cyclone as it moves inside its parent (coarse) domain.

*Note that the Vortex-following capability only works for tracking cyclones.

 

Note To run WRF for this case you will need to be in the "/glade/derecho/scratch/$USER/practice_exercises/wrf_vortex/" directory because the vortex–following option requires a different compilation; however, to run WPS, you will use the same standard build that you've used for most of the other exercises.

Set-up WPS

• For this exercise, you are running a case for the 2016 Hurricane Matthew event. Use the following information to modify namelist.wps.


• Make sure you are in the /glade/derecho/scratch/$USER/practice_exercises/wps directory.


• Create a single domain over the Gulf of Mexico - the nest will be added when you run WRF.


• The domain size will be 91 x 100 grid points, with a grid resolution of 27 km.


• Use a Mercator projection.


• Make the following changes to ensure the domain spans the correct location on the globe:
  

  ref_lat = 28.00
  ref_lon = -75.00
  truelat1 = 28.0,
  stand_lon = -75.00
  

• The dates for this simuation are 2016-10-06_00 to 2016-10-08_00. The data are from GFS and can be found in /glade/campaign/mmm/wmr/wrf_tutorial/input_data/matthew/ (prefix: gfs.0p25.2016100). Because this is GFS forecast data, it has a higher temporal resolution (available every 3 hours), and we should take advantage of that. In general, if higher time-frequency input data is available, that would be a better choice.




• Check that your domain is in the correct location. It should look like the picture below:

  

• Run the executables for the WPS program to create the necessary files for running wrf.
  
  

  Note To run ungrib.exe, it is typically okay to simply run it with the command "./ungrib.exe;", however, for this specific case, because there is a lot of data to process, NCAR's HPC system MAY give a segmentation fault when trying to run this command if the login nodes become saturated. To avoid this, try using the following (where UMMM0005 is the computing project we're working under): qcmd -A UMMM0005 -- ./ungrib.exe

 

Set-up and run WRF

• Make sure you are in the /glade/derecho/scratch/$USER/practice_exercises/wrf_vortex/test/em_real directory.    
   
• Edit namelist.input to reflect the appropriate domain/date information.
  
  

  Note You are running with 2 domains, although you only created one domain in WPS. Make sure the namelist components match those from WPS for d01. Listed below are the values you can use for d02.

  
   
  

  input_from_file = .true.,.false.,
  time_step = 150,
  max_dom = 2,
  e_we = 91, 88,
  e_sn = 100, 79,
  num_metgrid_levels = 32
  i_parent_start = 1, 25,
  j_parent_start = 1, 14,
  parent_grid_ratio = 1, 3,
  parent_time_step_ratio = 1, 3,
  

   

  Note Setting input_from_file=.false. for domain 2 indicates that you will NOT be creating input data (wrfinput_d02) for domain 2. The parent_start values are for the initial nest location. Make sure your vortex is inside the nest domain area at this time.




• Run real and wrf, as usual.


• Check your output.